Flow Velocity Measurement Using a Spatial Averaging Method with Two-Dimensional Flexural Ultrasonic Array Technology

Abstract

Accurate average flow velocity determination is essential for flow measurement in many industries, including automotive, chemical, and oil and gas. The ultrasonic transit-time method is common for average flow velocity measurement, but current limitations restrict measurement accuracy, including fluid dynamic effects from unavoidable phenomena such as turbulence, swirls or vortices, and systematic flow meter errors in calibration or configuration. A new spatial averaging method is proposed, based on flexural ultrasonic array transducer technology, to improve measurement accuracy and reduce the uncertainty of the measurement results. A novel two-dimensional flexural ultrasonic array transducer is developed to validate this measurement method, comprising eight individual elements, each forming distinct paths to a single ultrasonic transducer. These paths are distributed in two chordal planes, symmetric and adjacent to a diametral plane. It is demonstrated that the root-mean-square deviation of the average flow velocity, computed using the spatial averaging method with the array transducer is 2.94%, which is lower compared to that of the individual paths ranging from 3.65% to 8.87% with an average of 6.90%. This is advantageous for improving the accuracy and reducing the uncertainty of classical single-path ultrasonic flow meters, and also for conventional multi-path ultrasonic flow meters through the measurement via each flow plane with reduced uncertainty. This research will drive new developments in ultrasonic flow measurement in a wide range of industrial applications.

The High Frequency Flexural Ultrasonic Transducer for Transmitting and Receiving Ultrasound in Air

“…In addition to the transducer's response leading to lower amplitude detection signals and wave generation, the acoustic damping coefficients of air are approximately proportional to the second power of the frequency of the ultrasonic wave [30], making higher frequency operation challenging. One approach that has been used to increase signal amplitude with FUTs at higher frequencies has been to use flexural ultrasonic array transducers [26][27][28]. However, many applications require smaller, individual transducers with good sensitivity, and so a systematic approach is used in the development of a high frequency FUT (HiFFUT).…”

“…Thin piezoelectric discs (PZT-5H, PI Ceramic) with a thickness of 0.25 mm have been utilised in our previous FUT research [20,26,28], and are therefore chosen for this study. PZT discs of different diameters were modelled with a fixed thickness of 0.25 mm, bonded to the inside of the cap with a 0.1 mm thick layer of epoxy adhesive (Araldite 2014-1).…”

“…The FUT operates by vibrating at one of the resonant modes of the platepiezoelectric disc composite structure, with a relatively high transduction efficiency at low power and low voltage (<10 V) excitation. The simple structure is easy to manufacture, resulting in a low cost, mechanically robust transducer [20][21][22][23][24][25][26][27][28][29]. One of the principal limitations of the FUT has been the assumption that operating frequency is generally limited to below 50 kHz, with the most common operation frequency for commercially available FUTs being 40 kHz [21].…”

Multi-Angle Liquid Flow Measurement Using Ultrasonic Linear Array Transducer

“…The possible factors degrading the accuracy of our transit-time ultrasonic flowmeter were the small inner diameter and pipe roughness, as well as the velocity distribution in the pipe [11,13]. To increase measurement accuracy, a multipath approach was suggested in the previous study [16,28]. By using multipath rather than a single path, the increased sound path coverage can improve measurement accuracy.…”

“…In this study, 24 incidence angles were applied for both upstream and downstream transmissions. Then, the estimated flow rates were averaged, which is a similar concept as the spatial averaging method [28]. To measure the time difference, each plane wave angle had appropriate matching receiver elements for the transmitter elements in the upstream and downstream.…”